1. Field of the Invention
The present invention relates in general to a control apparatus for a vehicular hybrid-type power transmitting system including an electrically controlled differential portion and a step-variable transmission portion, and more particularly to techniques for reducing a possibility of interruption of deceleration of a vehicle in the process of a shift-down action of the step-variable transmission portion during coasting of the vehicle.
2. Discussion of Prior Art
There is known a vehicular power transmitting system including (a) an electrically controlled differential portion which has a differential mechanism and an electric motor connected to a rotary element of the differential mechanism and which is operable to control a differential state between rotating speeds of its input and output shafts by controlling an operating state of the electric motor, and (b) a step-variable transmission portion which constitutes a part of a power transmitting path between the electrically controlled differential portion and a drive wheel of a vehicle. JP-2006-213149A discloses an example of such a vehicular power transmitting system. The differential mechanism of the vehicular power transmitting system disclosed in this publication is provided with a differential-state switching device operable to switch the differential mechanism between a step-variable shifting state and a continuously-variable shifting state. The above-identified publication also discloses a control apparatus for the vehicular power transmitting system, which control apparatus is configured such that a selected one of an operation to switch the shifting state of the differential mechanism and an operation to start an engine is implemented prior to the other if the switching operation of the shifting state and the starting operation of the engine would otherwise overlap each other, so that a switching shock of the differential mechanism is reduced.
In a hybrid-type power transmitting system including an engine and an electric motor as disclosed in the above-identified publication, it is desirable to control the electric motor for synchronization of the output shaft speed of the differential mechanism with a synchronizing speed of a selected gear position of the step-variable transmission portion, for reducing a shift-down shock of the step-variable transmission portion in a shift-down action thereof during coasting of the vehicle. To effect this synchronizing control, it is necessary to temporarily place the step-variable transmission portion in a neutral state in the process of the shift-down action. In the neutral state of the step-variable transmission portion, however, there is a possibility of interruption of deceleration of the vehicle in the process of the shift-down action of the step-variable transmission portion, due to disconnection of the step-variable transmission from the drive wheel driven by a kinetic energy of the coasting vehicle, so that the vehicle operator may recognize the interrupted deceleration of the vehicle unexpectedly during the coasting run of the vehicle.